Apparatus for selectively displaying analogue quantities of plural input data signals

ABSTRACT

A display apparatus receives analogue signals representing the detected values of the number of revolutions per minute of an automobile&#39;s engine, the residual fuel, the automobile&#39;s speed, the temperature at the various portions of the automobile and the like. An analogue signal desired for display is selected from those analogue signals by means of a switching device. The selected signal is applied to a common terminal. A plurality of light emitting diodes are connected between the common terminal and the terminals of a voltage-dividing device consisting of a plurality of resistors thereby to display the detected values.

The present invention relates to a display apparatus for displayinganalogue quantities (input data) as the ratio of the analogue quantitiesto a predetermined value in the form of a graph. The display apparatusis adapted particularly to the instrument panel of vehicles such asautomobiles for display of analogue values representing the number ofrevolutions per minute of an automobile's engine, the temperature at thevarious portions of the automobile, the residual fuel and the like.

For displaying the detected ratio of the analogue input value (inputdata) to a predetermined value, a conventional display apparatus uses acircuit for comparing input data and another circuit for displaying thecomparison result of the input data. Since the conventional displayapparatus is provided with the display circuit and the comparing circuitseparately, it requires a number of circuit components which result in ahigh cost.

Accordingly, an object of the present invention is to provide a displayapparatus with a simple circuit construction.

Another object of the present invention is to provide a display circuitwith a comparing function.

Other object of the present invention is to provide a display devicewhich can receive input data and select a desired one from the inputdata thereby to display it.

This invention provides a single-circuit arrangement capable ofcomparing the selected input data signal with the reference valuepredetermined and then displaying the result of the comparison, so thatthe circuit arrangement is simple in construction.

In more particular, a datum selected from the input data is applied to afirst common terminal in the form of an analogue signal (voltage orcurrent). In order to cause the corresponding number of the lightemitting diodes to the analogue quantity of the selected input signal tolight up, the light emitting diodes receive each reference step voltage,which stepwisely changes, at the one-side terminals in accordance withthe order of the light emitting diodes set in array, while they receiveat the other-side terminals the voltage which has been applied theretoand now appears at the first common terminal. Current flows through thelight emitting diodes when they are forwardly biased by the potentialdifference appearing between the one-side terminals with the referencevoltage applied thereto and the other-side terminals with the input dataapplied thereto, so that such biased light emitting diodes make alight-emission.

There are two ways for displaying the input data: One is that the numberof light emitting diodes in light emitting state shows the analoguevalue of the input data; The other is that the number of light emittingdiodes in light non-emitting state indicates the analogue value. Theways are selectable with which electrode of the light emitting diodes isconnected between the terminals providing the reference step voltagesand the first common terminal, i.e. which terminal the anode of thelight emitting diode is connected to. The present invention permitseither electrode of the light emitting diodes to be connectable to thecommon terminal. When the anode of the light emitting diode is connectedto the common terminal, light is emitted from the light emitting diodeof the number corresponding to the analogue value if the reference stepvoltage is positive. Conversely, in the case of the cathode of lightemitting diode being connected to the common terminal, thelight-emitting diodes of the number corresponding to the analogue valueare turned off.

In this specification, the term "light emitting diode" is used to definea component which has at least two terminals and the impedance of whichlargely varies by the polarity of the voltage applied across the twoterminals thereof and emits light when the current flowing therethroughreaches a predetermined value.

The components of the name other than the above which are now or will becommercially available, are also applicable to the display apparatus ofthe present invention if they have the above-mentioned characteristic.Thus, such components must also be involved in the above term of "lightemitting diode".

Other objects and features of the present invention will be apparentfrom the following description taken in connection with the accompanyingdrawings, in which:

FIG. 1 shows a block diagram of an embodiment of a display apparatusaccording to the present invention; and

FIG. 2 shows a circuit diagram of a preferred embodiment of the blockdiagram of FIG. 1.

FIG. 1 shows a block diagram of a display apparatus of a preferredembodiment according to the present invention. In the figure, aswitching circuit 1 selects one of input data V₁ to V_(n). The selectedinput data is in turn transferred to a comparison and display circuit 5,while, at the same time, a signal for selecting the voltage determinedby the selected input data is fed to a reference-voltage productioncircuit 3.

The comparison and display circuit 5 compares the input data voltagefrom the switching circuit 1 with the output voltage from the referencevoltage production circuit 3. Through the comparing operation, when theinput data voltage is larger than the output voltage of the referencevoltage production circuit 3, the input data are displayed. When theabove relationship in amplitude between the input data voltage and thereference output voltage is reversed, the input data are not displayed.

FIG. 2 shows a concrete construction for a preferred embodiment of theblock diagram in FIG. 1. In FIG. 2, reference numeral 10 is a switchingsignal production circuit for producing switching signals S1 to Sn, 111to 11n and 121 to 12n designate switches which are turned on and off inresponse to switching signals S1 to Sn, 31 to 3 (m + 1) and 511 to 51mare resistors, 521 to 52m designate light emitting diodes, and E₁ toE_(n) are voltages determined by the input voltages V₁ to V_(n).

The switches 111 to 11n receive at the input side the input voltages V₁to V_(n), while they are at the output side connected to a commonterminal A. The common terminal A is connected to the anodes of thelight emitting diodes 521 to 52m, through resistors 511 to 51m.

The switches 121 to 12n receive at the input side the voltages E₁ toE_(n), and are at the output side connected in common to a seriescircuit consisting of resistors 31 to 3 (m + 1). The respective junctionpoints of the resistors 31 to 3 (m + 1) are connected to the cathodesides of the light emitting diodes, respectively. It will be noted herethat the voltages E₁ to E_(n) are produced by a combination of, forexample, a DC power source 41, resistors R₄, and diodes D₄. If thevariable range of each of the input voltages representing the input datais identical, a common voltage may be used for the voltages E₁ to E_(n).In this case, switches 121 to 12n become unnecessary.

In the circuit construction of FIG. 2, assume that the gth switches 11gand 12g are selected. Upon this switch selection, the switch 11gproduces an input voltage V_(g). The switch 12g produces the voltagedetermined by the input voltage V_(g), which is in turn fed to theresistors 31 to 3 (m + 1).

At this time, the output voltage V_(s31) to V_(s3m) appearing at thejunction points of the respective resistors 31 to 3 (m + 1) are given bythe equation (1) ##EQU1## where R₃₁ to R₃(m+1) are the resistance valuesof the resistors 31 to 3(m+1), respectively.

When the voltage V_(s3m) obtained by the equation (1) is set at themaximum value of the input voltage Vg selected by the gth switchingsignal, the voltage V_(s3m) corresponds to 100% of the maximum value ofthe input voltage.

Further, the resistance values of the resistors 31 to 3m are chosen sothat the voltages V_(s31) to V_(s3m) in the equation (1) will be thepredetermined ratios of voltage to the maximum value of the inputvoltage, respectively.

As described above, the input voltage V_(g) selected by the gth switch11g is outputed from the switch 11g and is compared with the voltagesV_(s31) to V_(s3m). When V_(g) < V_(s31) to V_(s3m), none of the lightemitting diodes 521 to 52m light up. On the contrary, when V_(g) >V_(s31) to V_(s3m), all of the diodes 521 to 52m light up.

If the voltage V_(g) is between the ith voltage V_(s3i) and the jthvoltage V_(s3j), i.e. V_(s3i) < V_(g) < V_(s3j), the light emittingdiodes 521 to 52i light up, while the diodes 52j to 52m do not light up.

As seen from the above, the light-emitting state of the respective lightemitting diodes shows what is the ratio of the input voltage V_(g) tothe maximum value of the input voltage. In the case where a higheraccuracy is required for display, the voltages V_(s31) to V_(s3m) areformed so as to satisfy such accuracy.

The resistors 511 to 51m are used for adjusting the current flowingthrough the corresponding light emitting diodes 521 to 52m thereby tomake the brightness of the respective light emitting diodes uniform.

It is assumed now that the input voltage Vg is between the ith voltageV_(s3i) and the jth voltage V_(s3j). One of the light emitting diodesfrom the first to the ith, for example, the diode 52i has the currentI_(52i) flowing therethrough which is given by the equation (2) ##EQU2##where r_(52i) and r_(51i) are the forward resistance of the photodiode52i and the resistance of the resistor 51i, respectively.

The numerator V_(s3i) of the right side of the equation (2) is variablefor the respective light emitting diodes. Therefore, in order to makeconstant the currents flowing through the respective light emittingdiodes, it is necessary to change the resistance values of the resistors511 to 51m. More particularly, as the voltage which a light emittingdiode indicates is closer to the maximum value of the input voltage, theresistor to be connected in series with the light emitting diode must besmaller in resistance. Assuming that the resistance values of resistors511 to 51m are r₅₁₁ to r_(51m), these resistance values are expressed asfollows: r₅₁₁ > r₅₁₂ > r₅₁₃ > . . . r_(51m).

The display apparatus heretofore described provides the useful effectsas given below.

(1) In the conventional display apparatus, the comparing circuit and theindicating circuit are separately provided. On the other hand, thedisplay apparatus according to the present invention is constructed suchthat the comparison and the display function can be achieved by a singlecircuit construction. Accordingly, necessary parts are saved.

(2) The saving of parts make it possible to increase the reliability ofthe apparatus and to reduce the cost thereof.

(3) Since the switches 111 to 11m are used, it is possible to display aplurality of input data.

In the embodiment of the display apparatus heretofore described, as theinput data increase, the number of the diodes in light-emitting state isincreased. As will be recalled, the display device according to thepresent invention may be constructed such that, with increase of theinput data, the number of the diodes in light-emitting state isconversely decreased. Such a construction is easily realized byreversing the connection of light emitting diodes in the direction sothat a direction of current flow through the light emitting diode isreversed.

The switching signal production circuit 10 in the above-mentionedcircuitry is composed of, for example, a DC power source 14, a resistorR₁, diodes D₁, switches SW₁ to SW_(n). An operator such as anautomobile's driver turns on one of the switches SW₁ to SW_(n). Byturning-on of the switch, the corresponding switches are selected fromthe groups of the switches 111 to 11n and 121 to 12n. When the presentinvention is applied to the automobile, another control means may beused for producing the switching signals S₁ to S_(n). The control meansmay be registers, ring counters and the like which comprise flip-flopscommonly used as digital circuit elements. Semiconductor switches mayalso be used for the switches SW₁ to SW_(n). These digital circuitelements may be arranged so as to be operable in response to othercontrol signals.

The circuit of the preferred embodiment mentioned above is constructedto be adapted to the automobile in which automobile's speed, watertemperature, residual fuel make up the bulk of the input data. Thedetecting means for the input data completely differs depending on thevariety of the input data to be detected. Accordingly, the variablerange of the output voltage and the amplitude thereof also differdepending on the variety of the input data. It is for this reason thatthe arrangement is employed in which the input voltage applied to thevoltage-dividing circuit consisting of resistors 31 to 3 (m + 1) ischanged over within the range of E₁ to E_(n) by means of switches 121 to12n. It is noted that if the variable range of each of the inputvoltages V₁ to V_(n) is identical, the voltages E₁ to E_(n) may be thesame in magnitude. In this case, the switches 121 to 12n becomeunnecessary.

What is claimed is:
 1. An apparatus for selectively displaying analoguequantities of plural input data signals, comprising:a plurality of inputmeans for receiving a corresponding plurality of input voltages of saiddata signals; first switching means having a plurality of inputterminals connected to said input means and having an output terminalfor selectively providing one of said input voltages; reference voltagegenerating means for generating a plurality of reference voltagescorresponding to said data signals; second switching means having aplurality of input terminals connected to said reference voltagegenerating means and having an output terminal for selectively providingone of said reference voltages corresponding to said one of inputvoltages selected by said first switching means; voltage dividing meanshaving an input terminal connected to said second switching means andhaving a plurality of output terminals, for dividing the selected one ofreference voltages into a plurality of predetermined different voltages,and respective output terminals being provided for said respectivepredetermined different voltages; means for generating a plurality ofswitching signals for driving said first and second switching means andfor selectively providing one of said switching signals to said firstand second switching means; and display means including a plurality oflight emitting diodes each connected between the output terminal of saidfirst switching means and a respective output terminal of said voltagedividing means for providing a luminant display for the selected one ofsaid input data signals.
 2. An apparatus for selectively displayinganalogue quantities of plural input data signals according to claim 1,wherein said voltage dividing means comprises a plurality of resistorsconnected in series, and said light emitting diodes are connectedbetween the output terminal of said first switching means and respectivejunction points of said resistors.